[plug] lightning, Re: modem

[Gavin Chester]

On Wed, 2006-06-14 at 15:23 +0800, Michael Holland wrote:

> Would I be right in guessing that the telephone system is good at
> collecting surges from lightning strikes over a large area, while the TV
> antenna will only collect very near strikes, so is less likely to do
> damage? (But when it does...)

Hmm, maybe :-/  But what about your overhead power lines?  Lightning
strikes are very unpredictable, as you might imagine. Witness these
tales: 

Several years ago, I had ONE appliance in a house (a VCR) that had it's
main board fried by nearby lightning.  It only had a power connection,
no aerial.  All other devices in the house were untouched, including the
TV sharing a power board with that VCR.

Similarly, I recently had ONE telephone device fried out of all the PCs
and fax/answering machines and cordless phones that have a connection to
the two phone lines coming to my house.  It was in parallel with other
devices but got picked out for special attention.

I recently suffered 8 days without phone lines because of an electrical
storm that passed straight over Dwellingup.  The Telstra technicians
said that extensive lengths of buried cable were literally "blown up" in
their trenches! :-O.  One spot was so bad that the technicians claimed
that a concrete lid on an inspection pit was blown about 10m away from
the pit!  While all this was happening, houses in the same street were
randomly singled out for attention, with some people having the sockets
blown apart off their wall (to quote the technicians, again) while
others were smiling because they had no household damage.

I live on a small acreage in the forest and have trees around me within
10m of the house that have taken direct lightning hits.  These
eventually die, but in the meantime the bark is blown off the side of
the tree like a zipper being undone.  Funny thing is that the trees that
were hit are not the tallest in that spot :-/.  While all that was going
on, my metal-roofed house escaped unscathed, even though it cries out,
"zap me", and overhead power lines terminate at my house after a long,
rambling run through the trees.

So, you can take precautions, but in the end a large measure of luck
prevails.  Look into the work of Ben Franklin, he has saved people
billions of dollars over past generations with his pioneering work on
lightning conductors :-)

It's all interesting stuff.

Gavin